Competition and the evolution of aggressive behavior in two species of terrestrial salamanders.

Plethodon jordani and P. glutinosus are closely related, ecologically similar species that are sympatric at intermediate elevations in the S Appalachian Mountains. Interspecific competition is more intense in the NE Great Smoky Mountains, where the species are narrowly sympatric, than in the nearby Balsam Mountains, where sympatry is broader. In laboratory encounters, P. glutinosus from the Great Smoky Mountains were more aggressive to heterospecific and conspecific intruders than were P. glutinosus from the Balsam Mountains. For P. jordani, however, the variation in interspecific and intraspecific aggressive behavior among individuals within populations was as great as the variation between populations. Alpha-selection (ie improved competitive ability by the acquisition of interspecific interference mechanisms) has occurred in populations of P. glutinosus under conditions of intense interspecific competition. The evolution of aggressive behavior also appears to have been influenced by the intensity of intraspecific competition. -from Author